It is known in the art of lubricant additives and plasticizers for polyvinyl chloride (PVC) that epoxidized fatty acid esters exhibit very desirable properties, especially when there is a moderately high degree of unsaturation within the starting fatty acid chain. After epoxidation, the “oxirane” value is a key factor correlating significantly to performance. This is the weight ratio of the oxygen atoms added across the double bonds, usually chemically depicted as:

See for example Wickson, Edward J., ed; Handbook of Polyvinyl Chloride Formulating, (John Wiley & Sons), pgs 253-273. Performance characteristics of various epoxy plasticizers have been detailed on pages 258 through 271 in the Wickson book. Table 7.9 in Wickson provides a useful summary of relative performance characteristics. Epoxidized monoesters, such as octyl epoxytallate, exhibit some favorable plasticizers properties, especially low-temperature flex and desirable plastisol rheology, but are not so good in other respects. According to the data (Table 7.9 in Wickson), the bis-epoxy esters appear to offer the best overall blend of performance attributes. Ignoring the cost rating relevant to the publication period, it is near the best in almost all categories. Table 7.8 in Wickson indicates even unexpected good performance in plastisols. Table 7.3 in the reference presents evidence that bis-epoxides can offer performance as good as or better than di-isodecyl phthalate (DIDP). In addition, it is stated on page 262 of Wickson that bis-epoxides provide superior resistance to spew in the critical “window exposure test”.
The oxirane percent also appears to be a factor to consider for certain performance attributes, and that can be varied and controlled by the selection of the fatty acids used in building the bis-epoxide molecules. With epoxidized soybean oil (ESO), one is limited to whatever the soybean oil allows. On the other hand, if one isolates then epoxidizes an isononyl ester of linolenic acid, the resultant product has almost an 11 percent oxirane content. Certain seeds, flax and camelina for example, contain a relatively high percentage of linolenic acid glycerides. The very common methanolysis to produce biodiesel offers a ready source of fatty acid monoesters that can be distilled into the desired fractions.
World Patent Application WO0198404 also provides some useful comparisons of properties for various epoxy plasticizers. They call the one bis or diester “epoxidized propylene glycol disoyate”. The viscosity for this diester plasticizer at ˜180 cP is quite favorable compared to ˜440 cP for ESO (a fatty acid triester). This facilitates cold weather handling and also fusion with the PVC powder. U.S. Pat. No. 5,643,501 also reports exceptional performance in plasticized PVC from essentially the same material, which is referred to as a secondary stabilizer that the '501 patent calls propylene glycol bis(epoxy oleate).
Besides the bis-epoxides, epoxidized monoglyceride diacetates have been shown to provide some favorable plasticizer properties. See, for example, U.S. Pat. Nos. 2,895,966, and 7,071,343. The performance data available is not nearly as extensive for the monoglyceride diacetates as for the bisepoxides. Actually, epoxidized diglyceride monoacetates would be structured molecularly much like the bis-epoxides.
While these bis-epoxide and glyceride-acetate plasticizers and their favorable performance have been known and offered commercially for many years, extensive commercialization has presumably been hampered mostly by cost considerations, but with record crude oil prices appearing in 2007, that situation is shifting. The doubling of U.S. biodiesel capacity in 2007 alone has made methyl esters of a few types of fatty acids readily available in large quantities in a very competitive marketplace. Meanwhile, a potential major use of the byproduct glycerin has emerged in the form of propylene glycol processes. Epoxidized vegetable oils have long had important industrial uses, but relatively high viscosity and a tendency to exude from plasticized PVC has limited their use as primary plasticizers.
While favorable performance is an important consideration for commercial use, achieving widespread use as a commodity plasticizer depends greatly on the cost relative to competing products of similar performance. In the overall economics of epoxy ester production, an economical source of hydrogen peroxide is a very important factor, as it is a key reactant in the epoxidation reaction. It typically will account for about 20 wt % of the raw material. Besides cost, storage and transportation of the required concentrated hydrogen peroxide solutions presents significant safety concerns, especially in light of recent terrorist threats. The fatty acid portion of the molecules still accounts for approximately 80 percent by weight, so that cost is of course a major consideration. As previously mentioned, biodiesel fuel or fractions thereof can be an economic source of the fatty acid portion, particularly if made from lower-value reclaimed waste feedstocks instead of virgin refined vegetable oils.
The most prevalent process for production of hydrogen peroxide involves the cyclic oxidation and reduction of a working compound such as an alkyl anthrahydroquinone with concurrent formation of hydrogen peroxide and the corresponding anthraquinone. Two of the earliest disclosures of this technology were by Reidl in U.S. Pat. Nos. 2,158,525 and 2,215,883. The oxygen atoms in the hydrogen peroxide molecule ultimately come from oxygen in the atmosphere, but a regenerable oxygen carrier molecule is typically needed to generate the hydrogen peroxide molecules. The anthraquinone or other oxygen carrier is subsequently hydrogenated to regenerate the starting anthrahydroquinone, which is then recycled to oxidation. Although the bulk of the reagent is recycled continuously through the process, it is necessary to provide a make-up stream to replace the inevitable losses of regenerable working compound in the process. This issue of formation and removal of inert byproducts was addressed by Sethi in U.S. Pat. No. 4,824,609. The ethyl anthraquinone used in the most common industrial process is an expensive material, so even a small make-up stream to the recycle can be a significant expense. In addition, there is significant working capital tied up as part of the in-process inventory.
U.S. Pat. Nos. 4,897,252, 5,254,326, and others by the same inventors, describe a similar process that uses oxidation of a secondary alcohol, methylbenzyl alcohol (MBA), to make hydrogen peroxide (H2O2), and byproduct acetophenone results. In the process, the byproduct acetophenone is hydrogenated back to MBA, which is subsequently recycled to oxidation. The methylbenzyl alcohol is a much less expensive material than the substituted anthraquinones; however, the recovery and separation steps of the MBA-based process are considerably involved, with steps of stripping, extraction, and distillation being necessary to make it practical. This is a consequence of the secondary alcohol with a normal boiling point near 200 C having a significant volatility relative to the hydrogen peroxide, which has an atmospheric boiling point close to 150 C. Although the MBA/acetophenone process is substantially different than that of the instant invention, favorable oxidation conditions for secondary alcohols have been disclosed and are incorporated herein by reference.
Epoxidation of ethylenically unsaturated compounds, specifically light olefins such as ethylene and propylene, in combination with hydrogen peroxide production, is discussed extensively in the prior art literature. Among these are a series of patents assigned to Arco Chemical Technology, including U.S. Pat. Nos. 4,897,252, 5,166,372, 5,214,168, and 5,463,090. The hydrogen peroxide produced in the processes of these three patents is fed, still combined with its working solution, to the epoxidation reactor along with the olefin substrate, typically propylene. Consequently, an additional separation step is needed to remove the product from the regenerable working material and other epoxidation reaction constituents. This necessitates additional equipment and expense. The Arco process is tailored to light olefins only, ones yielding product which can be stripped out readily after the epoxidation.
Similarly, an integrated process for epoxidation of lighter olefins is disclosed in U.S. Pat. No. 6,822,103. Highly corrosive HBr is used in generation of the hydrogen peroxide by feeding oxygen-containing gas into a predominately volatile methanol mixture. The resulting 9.3% hydrogen peroxide solution was used for epoxidation of either octene or propylene in the presence of a volatile solvent. There is no indication that solvent recoveries and separation would be commercially feasible. As with the Arco process, light olefins are the main target.
U.S. Pat. No. 4,303,632 by Gosser discloses promising oxidation results for another secondary alcohol system, that of diphenylcarbinol (benzhydrol) and benzophenone. However, under the conditions described by Gosser, the reported yields were far from what would be practical for commercialization. The viability and conditions for the necessary hydrogenation of benzophenone to diphenylcarbinol were disclosed in U.S. Pat. No. 4,302,435. However, it is not obvious how the benzophenone system could be made practical, and there is no knowledge of any later efforts to further develop or commercialize this method. The initial charge and makeup benzophenone material are relatively inexpensive.